Low pressure gas-filled discharge device having an envelope comprising metal parts at different potentials in operation insulated from one another by ceramic members



Aug. 15, 1967 B. o. BAKER ETAL 3,335,492

LOW PRESSURE GASFILLED DISCHARGE DEVICE HAVING AN ENVELOPE COMPRISING METAL PARTS AT DIFFERENT POTENTIALS IN OPERATION INSULATED FROM ONE ANOTHER BY CERAMIC MEMBERS Filed Oct. 21, 1964 2O FITTO'RN e s United States Patent 3,336,492 LOW PRESSURE GAS-FILLED DISCHARGE DE- VICE HAVING AN ENVELOPE COMPRISING METAL PARTS AT DIFFERENT POTENTIALS IN OPERATION INSULATED FROM ONE AN- OTHER BY CERAMIC MEMBERS Basil Otfor Baker, Croxley Green, and Robert Joseph Wheldon, Chalfont St. Peter, England, assignors to The M-O Valve Company, Limited, London, England Filed Oct. 21, 1964, Ser. No. 405,559 Claims priority, application Great Britain, Oct. 25, 1963, 42,297/ 63 8 Claims. (Cl. 313190) This invention relates to gas-filled electric discharge devices. I The invention relates particularly to electric discharge devices of the kind wherein the gas filling is at a low pressure, that is to say a pressure on the left hand side of the Paschen curve for the gas constituting the filling, and wherein the gas filling is contained by an envelope comprising: at least two metal parts which are respectively electrically connected to electrodes of the device which may be at very different electric potentials in operation of the device; and a ceramic member sealed between each pair of said metal parts of the envelope to insulate said metal parts from one another.

In such a device the making of external electrical connections to those electrodes connected to metal parts of the envelope is clearly facilitated.

In designing the envelope of a device of the kind specfied above, certain problem arise.

Firstly, in view of the low pressure of gas filling, the length of the path via the gas filling between opposed metal parts of the envelope which may be at different potentials in operation must not exceed a certain maximum value in order to avoid unwanted electrical breakdown, while at the same time the shortest distance between metal parts of the envelope insulated from one another by a ceramic member via the surface of that ceramic member must be relatively long.

Secondly, the internal surface of each ceramic member must be positioned well away from, or shielded from, the path of the main discharge in the device to reduce the possibility of a serious reduction in the electrical resistance of paths alongthe internal surface of each such ceramic member due to sputtering.

In our United States Patent No. 3,130,344 there is disclosed an electric discharge device of the kind specified whose envelope includes two metal parts which are respectively at different electrode potentials in operation wherein the above-mentioned problems are overcome.

It is an object of the present invention to provide an electric discharge device of the kind specified wherein the above-mentioned problems are overcome, which device has an envelope that includes three metal parts which are respectively at different electrode potentials in operation.

According to the present invention in an electric discharge device having an envelope containing a low pressure gas filling and housing an electrode system including an anode, a cathode, and a further electrode disposed between the anode and the cathode, the envelope comprises: a first tubular metal portion which houses the cathode and has an outwardly extending flange at one end, said portion of the envelope being at least approximately at the same potential as the cathode in operation; a second tubular metal portion which houses and is electrically connected with the further electrode, and is disposed coaxial with said first tubular metal portion of the envelope and has an outwardly extending flange adjacent its end nearer said first metal portion, the adjacent faces of said flanges being closely spaced; a first tubular ceramic member which coaxially surrounds said first and second metal portions of the envelope; first and second metal sealing ring means whereby the ends of the first ceramic member are respectively sealed to the outwardly extending flanges, at least one of said first and second sealing ring means including a tubular portion disposed within the first ceramic member with its outer curved surface closely spaced from the internal surface of the ceramic member so that the length of the shortest path between the first and second sealing ring means along the surface of the ceramic member is relatively long compared with the shortest path via the gas-filling between said outwardly extending flanges; a second tubular ceramic member disposed coaxial with said second metal portion of theenvelope on the side of said second metal portion remote from said first metal portion of the envelope and having its end nearer said second metal portion sealed to the adjacent end of said second metal portion; a metal closure member which is electrically connected to the anode and hermetically seals the other end of the second ceramic member; at least one of said second metal portion of the envelope and the metal closure member including a tubular portion disposed within the second ceramic member with its outer curved surface closely spaced from the internal surface of the second ceramic member so that the length of the shortest path between said second metal portion of the envelope and the metal closure member along the surface of the second ceramic member is relatively long compared with the shortest path via the gas filling between the metal closure member and said second metal portion of the envelope; and means hermetically sealing the end of said first metal portion of the envelope remote from said second tubular metal portion of the envelope.

In an electric discharge device in accordance with the invention the provision of tubular metal portions of the envelope disposed Within the ceramic members over-- comes the first of the above-mentioned problems, and the disposition of the ceramic members at positions relatively remote from the discharge path between the anode and cathode overcomes the second of the above mentioned problems.

One arrangement in accordance with the invention will now be described, by way of example, with reference to the accompanying drawing which is a part-sectional view of a thyratron having a peak inverse and forward holdoff voltage rating of kilovolts.

Referring to the drawing, the valve has a sealed envelope 1 filled with deuterium at a pressure of 0.3 millimetre of mercury.

The main body of the envelope is in the form of a hollow, generally cylindrical, metal structure incorporating two tubular metal members 2 and 3 which respectively have lengths of 3.644 inches and 1.30 inches and which are disposed coaxially so as to overlap by 0.3 inch, the overlapping portions of the members 3 and 2 respectively having an internal diameter of 2.875 inches and an external diameter of 2.470 inches. The members 2 and 3 are coaxially surrounded by a tubular ceramic member 4 of length 2.50 inches and internal diameter 4.10 inches, the ends of the member 4 being respectively joined via separate metal sealing ring arrangements to two outwardly extending flanges 5 and 6 formed on the members 2 and 3 respectively. The flanges 5 and 6 are positioned so that their opposed faces are spaced 0.18 inch apart with the face of the flange 5 nearer the flange 6 at a distance of 0.60 inch from the end of the member 2 within the member 3. The external surface of the member 4 has formed on it a series of equally spaced circumferential ribs 7 of square cross section.

The two sealing ring arrangements are identical, so that the member 4 is symmetrically positioned with respect to the flanges 5 and 6, and each includes a short tubular member 8 having at one end an inwardly extending flange which is sealed between the appropriate end surface of the member 4 and a ceramic backing ring 9, the tubular portion of the member 8 extending away from and being coaxial with the member 4. Each sealing ring arrangement further includes a thin-walled metal member 10 comprising two coaxial tubular portions of different diameters. The outer surface of the wider portion of each member 10 is sealed to the inner surface of the tubular portion of the appropriate one of the members 8, with the edges of the members 8 and 10 in register, and the narrower portion of the member 10, which has an external diameter slightly less than the internal diameter of the member 4, is disposed coaxially within the member 4, the free end of this narrower portion being sealed to the appropriate one of the flanges 5 and 6.

The member 3 is provided at its end remote from the member 2 with an inwardly extending flange 11, and a thin-walled metal tubular member 12 is secured to the inner edge of the flange 11, the member 12 being disposed coaxial with the envelope 1, and extending away from the member 3. The member 12 extends a distance of 0.813 inch beyond the flange 11 and has an external diameter of 1.362 inches. The member 12 is coaxially surrounded by a tubular ceramic member 13 which is sealed to the adjacent main face of the flange 11 by means of a sealing ring 14, the ring 14 comprising a short tubular member of length 0.25 inch having an inwardly extending flange 15 at one end, which is sandwiched between the end surface of the member 13 and a ceramic backing ring 16, and an outwardly extending flange 17 at its other end which is sealed to the flange 11. The member 13 has a length of 2.5 inches and an internal diameter of 1.406 inch and has its external surface ribbed in the same manner as the member 4. At its end remote from the flange 11, the member 13 is sealed to a thinwalled, metal closure member 18 comprising two coaxial tubular portions of external diameters 1.360 inches and 1.008 inches respectively and lengths 1.75 inches and 0.312 inch respectively. The two tubular portions are joined by an intermediate frusto-conical portion of length 0.817 inch and the wider tubular portions has an outwardly extending flange 19 formed at its free end. The flange 19 is sandwiched between the end surface of the member 13 and a ceramic backing ring 20 and the remainder of the closure member 18 is disposed coaxially within the ceramic member 13. A number of small protuberances 21 are formed half way along the length of the wider portion of the member 18 at equally spaced positions around the outer surface of the member 18, the protuberances contacting the internal surface of the member 13 and thus serving to inhibit movement of the member 18 within the member 13.

The electrode system of the thyratron is housed within the main body of the envelope 1 and comprises a main anode 22, an auxiliary anode 23, a control electrode 24 and a cathode 25.

The anode 22 is in the form of a metal disc of diameter 2.557 inches which is disposed adjacent the flange 11 with its main faces perpendicular to the axis of the envelope 1, the spacing between the anode 22 and the flange 11 being 0.177 inch. The anode 22 is supported at one end of a hollow metal rod 26 which serves as a lead to the anode 22, and extends perpendicularly away from the anode 22 coaxially through the ceramic member 13. The rod 26 has an external diameter of 1.00 inch for a distance of 0.860 inch from the anode 22 and an external diameter of 0.969 inch over the remainder of its length. The internal surface of the narrower portion of the closure member 18 is sealed to the external surface of the rod 26, thus completing the envelope of the valve.

The auxiliary anode 23 is in the form of a metal disc of diameter 2.920 inches and thickness 0.078 inch and has formed in it two symmetrically positioned arcuate slots 27, each slot 27 having a width of 0.098 inch and having its inner edge at a diameter of 1.966 inches. The auxiliary anode 23 is sealed around its periphery to the internal surface of the member 3 with its main faces perpendicular to the axis of the envelope and With the opposed main faces of the main and auxiliary anodes 22 and 23 separated by 0.177 inch.

The control electrode 24 comprises three metal discs 28, 29 and 30 of diameter 2.387 inches sandwiched together and sealed into the end of the member 2 within the member 3, the exposed main face of the upper disc 28 (with reference to the drawing) being in the plane of the end of the member 2 and spaced 0.187 inch from the adjacent main face of the auxiliary anode 23. The discs 28, 29 and 30 have thicknesses of 0.039 inch, 0.157 inch and 0.039 inch respectively and each disc 28, 29 or 30 has formed in it two symmetrically positioned, arcuate slots 31, 32 or 33 the slots 31, 32 and 33 having widths of 0.098 inch, 0.650 inch and 0.315 inch respectively and having their inner edges at diameters of 0.983 inch, 0.945 inch and 1.575 inches respectively.

A baflle 34 in the form of a metal disc of diameter 1.457 inches is disposed on the side of the control electrode 24 remote from the anode 22. The baffle 34 is secured to the disc 30 by means of a support 35 of electrical insulating material and is disposed, with its main faces perpendicular to the axis of the envelope 1, at a distance of 0.15 inch from the disc 30.

The cathode 25 is housed in the lower end of the main body of the envelope 1 and is of a type described in our copending patent application No. 272,074. The cathode 25 essentially comprises a hollow cylindrical member made of an electron emitting material in which is housed an electrical heater (not visible). The cathode 25 is supported coaxially within a metal heat shield 36 which is generally tubular in shape, but at its upper end, just beyond the cathode 25, narrows to provide a frustoconical portion 37. At its lower end the heat shield 36 is secured to a ceramic disc 38 which extends across the lower end of the main body of the envelope 1.

From the tubular portion of the heat shield 36 a series of equally spaced rectangular metal fins 39 project radially inwards, the fins 39 extending about two-thirds of the way along the length of the heat shield 36 from the frusto-conical portion 37. The internal surface of the heat shield 36 and the surfaces of the fins 39 are coated with electron emissive material derived from the cathode 25, deposition of this material being effected during manufacture of the valve.

A number of holes 40 are formed in the lower part of the heat shield 36 to reduce conduction of heat from the fins 39 to the ceramic disc 38.

Leads 43 to the cathode 25, the cathode heater, the baflle 32 and a heating element incorporated in the replenisher are sealed through the end wall of the compartment 41. Connection to the control electrode 24 is made via the member 2 and to the auxiliary anode 23 via the member 3.

In operation of the valve a discharge passes between the cathode 25 and the main anode 22 via the apertures 31, 32 and 33 in the control electrode 24 and the apertures 27 in the auxiliary anode 23. The fins 39 and the internal surface of the heat shield 36 contribute a major part of the total current when the valve is arranged to pass short pulses.

The anode voltage is applied to the thyratron by means of a resistive potentiometer connected between the main anode 22 and the cathode 25 and having a tapping point connected to the auxiliary anode 23 so that the potential of the auxiliary anode 23 with respect to the cathode 25 is half the potential of the main anode 22 with respect to the cathode 25 when no discharge is passing between the anode 22 and cathode 25. The control electrode 24 is maintained at substantially the same potential as the cathode 25.

It will be appreciated that the member 4 serves to insulate from one another the parts of the envelope 1 which are respectively at the control electrode potential and the auxiliary anode potential, and that the member 13 similarly insulates from one another the parts of the envelope respectively at the auxiliary anode potential and the main anode potential. Since, in the valve described above, the gas filling is at a pressure corresponding to a point on the left hand side of the Paschen curve for deuterium, the length of the path via the gas filling between opposed metal parts of the envelope 1 that are of different potentials, in operation, must not exceed a certain maximum value in order to enable the required anode voltage ratings to be obtained; at the same time, however, the shortest distance between the parts of the envelope 1 insulated from one another by the member 4 or 13 via the internal surface of that member 4 or 13 must be relatively long. These two requirements are satisfied in the valve described above by arranging for the metal parts of the envelope 1 on both sides of each of the members 4 and 13 to include tubular portions disposed within the members 4 and 13 which overlap closely the internal surfaces of the members 4 and 13 without touching them so that the distance between those metal parts is below the above mentioned maxi-mum value.

The shortest path between the parts of the envelope 1 insulated from one another by a member 4 or 13 via the external surface of that member 4 or 13 must also be relatively long. This is facilitated in the valve described above by'the provision of ribs on the members 4 and 13.

It will be noticed that the members 4 and 13 are both positioned well away from the main path of the discharge between the anode 22 and the cathode 25. This virtually eliminates the possibilities of a serious reduction in the electrical resistance of paths along the internal surfaces of the members 4 and 13 due to sputtering of material from the cathode 25 onto these surfaces.

It is pointed out that the auxiliary anode 23 and the control electrode 24 are respectively in good thermal contact with the members 3 and 2. Heat produced at these electrodes is consequently rapidly conducted away. Outwardly extending radial cooling fins may be provided on the external surface of the members 2 and 3 if desired.

We claim:

1. An electric discharge device comprising:

(A) a sealed envelope [1] including:

(1) a first tubular metal portion [2] having an outwardly extending flange [5] adjacent one end, said first tubular metal portion and said flange having exterior surfaces exposed on the outside of the envelope,

(2) a second tubular metal portion [3] disposed coaxial with said first tubular metal portion and having an outwardly extending flange [6] adjacent its end nearer said first metal portion, the adjacent faces of said flanges being closely spaced, said second tubular metal portion and said outwardly extending flange associated therewith having exterior surfaces exposed on the outside of the envelope,

(3) a first tubular ceramic member [4] which at least partly coaxially surrounds said first and second metal portions of the envelope,

(4) first and second metal sealing ring means [8, 10'] whereby the ends of the first ceramic member are respectively sealed to the outwardly extending flanges,

(5) at least one of said first and second sealing ring means including a tubular portion [10] disposed within the first ceramic member with its outer curved surface closely spaced from the internal surface of the ceramic member so that the length of the shortest path between the first and second sealing ring means along the surface of the ceramic member is relatively long compared with the shortest path via the interior of the sealed envelope between said outwardly extending flanges, said tubular portion having its exterior surface exposed on the outside of the envelope,

(6) a second tubular ceramic member [13] disposed coaxial with said second metal portion of the envelope on the side of said second metal portion remote from said first metal portion of the envelope having its end nearer said second metal portion sealed to the adjacent end of said second metal portion,

(7) a metal closure member [18] hermetically sealing the other end of the second ceramic member,

(8) at least one of said second metal portion of the envelope and the metal closure member including a tubular portion disposed within the second ceramic member with its outer curved surface closely spaced from the internal surface of the second ceramic member so that the length of the shortest path between said second metal portion of the envelope and the metal closure member along the surface of the second ceramic member is relatively long compared with the shortest path via the gas-filling between the metal closure member and said second metal portion of the envelope,

(9) means [41] hermetically sealing the end of said first metal portion of the envelope remote from said second tubular metal portion of the envelope;

(B) a gas filling within the envelope at a low pressure;

and

(C) an electrode system housed within the envelope including:

(1) a cathode [25] housed within said first tubular metal portion of the envelope, said first metal portion being at least approximately at the same potential as the cathode in operation of the device,

(2) an anode [22] housed within said second tubular metal portion of the envelope and electrically connected to said metal closure member,

(3) a further electrode [23] housed within said second tubular metal portion of the envelope between the anode and cathode, and electrically connected with said second metal portion of the envelope.

2. A discharge device according to claim 1 wherein both said first and second sealing ring means include a V said tubular portion disposed within the first ceramic member.

3. A discharge device according to claim 1 wherein at least at its end adjacent said second tubular metal portion of the envelope, said first tubular metal portion of the envelope is of smaller diameter than, and is disposed within, said second metal portion of the envelope.

4. A discharge device according to claim 1 wherein the further electrode constitutes an auxiliary anode and the electrode system also includes a control electrode [24] disposed in, and in electrical contact with, the first tubular metal portion of the envelope between the cathode and the auxiliary anode.

5. A discharge device according to claim 1 wherein said further electrode is mounted in good thermal contact with the second metal tubular portion of the envelope.

6. A discharge device according to claim 1 wherein ribs [7] are formed on the outer surface of at least one of said first and second ceramic members.

7. A discharge device according to claim 1 wherein the second tubular metal portion of the envelope is provided with an inwardly extending flange [11] adjacent its end 7 8 nearer the second ceramic member to which the adjacent References Cited end oft seccind ceramic mem[b1e4r] is hermetically sealed UNITED STATES PATENTS V13. a ir sea mg ring means 8. A discharge device according to claim 7 wherein g 13 1 1 said second tubular metal portion of the envelope includes 5 79,916 2; o ,E 3' X a said tubular portion which is disposed within the second i005, 24 10/ Rel y 31 190 X ceramic member which is constituted by a tubular metal member [12] secured to the inner edge of said inwardly JAMES LAWRENCE P'lmary Examiner extending flange. STANLEY D. SCHLOSSER, Examiner. 

1. AN ELECTRIC DISCHARGE DEVICE COMPRISING: (A) A SEALED ENVELOPE (1) INCLUDING: (1) A FIRST TUBULAR METAL PORTION (2) HAVING AN OUTWARDLY EXTENDING FLANGE (5) ADJACENT ONE END, SAID FIRST TUBULAR METAL PORTION AND SAID FLANGE HAVING EXTERIOR SURFACES EXPOSED ON THE OUTSIDE OF THE ENVELOPE, (2) A SECOND TUBULAR METAL PORTION (3) DISPOSED COAXIAL WITH SAID FIRST TUBULAR METAL PORTION AND HAVING AN OUTWARDLY EXTENDING FLANGE (6) ADJACENT ITS END NEARER SAID FIRST METAL PORTION, THE ADJACENT FACES OF SAID FLANGES BEING CLOSELY SPACED, SAID SECOND TUBULAR METAL PORTION AND SAID OUTWARDLY EXTENDING FLANGE ASSOCIATED THEREWITH HAVING EXTERIOR SURFACES EXPOSED ON THE OUTSIDE OF THE ENVELOPE, (3) A FIRST TUBULAR CERAMIC MEMBER (4) WHICH AT LEAST PARTLY COAXIALLY SURROUNDS SAID FIRST AND SECOND METAL PORTIONS OF THE ENVELOPE, (4) FIRST AND SECOND METAL SEALING RING MEANS (8, 10) WHEREBY THE ENDS OF THE FIRST CERAMIC MEMBER ARE RESPECTIVELY SEALED TO THE OUTWARDLY EXTENDING FLANGES, (5) AT LEAST ONE OF SAID FIRST AND SECOND SEALING RING MEANS INCLUDING A TUBULAR PORTION (10) DISPOSED WITHIN THE FIRST CERAMIC MEMBER WITH ITS OUTER CURVED SURFACE CLOSELY SPACED FROM THE INTERNAL SURFACE OF THE CERAMIC MEMBER SO THAT THE LENGTH OF THE SHORTEST PATH BETWEEN THE FIRST AND SECOND SEALING RING MEANS ALONG THE SURFACE OF THE CERAMIC MEMBER IS RELATIVELY LONG COMPARED WITH THE SHORTEST PATH VIA THE INTERIOR OF THE SEALED ENVELOPE BETWEEN SAID OUTWARDLY EXTENDING FLANGES, SAID TUBULAR PORTION HAVING ITS EXTERIOR SURFACE EXPOSED ON THE OUTSIDE OF THE ENVELOPE, (6) A SECOND TUBULAR CERAMIC MEMBER (13) DISPOSED COAXIAL WITH SAID SECOND METAL PORTION OF THE ENVELOPE ON THE SIDE OF SAID SECOND METAL PORTION REMOTE FROM SAID FIRST METAL PORTION OF THE ENVELOPE HAVING ITS END NEARER SAID SECOND METAL PORTION SEALED TO THE ADJACENT END OF SAID SECOND METAL PORTION, (7) A METAL CLOSURE MEMBER (18) HERMETICALLY SEALING THE OTHER END OF THE SECOND CERAMIC MEMBER, 